Silicide processes have been used to improve the conductivity of polysilicon gate and source/drain regions at the transistor level of an integrated circuit. The silicide layer provides a good ohmic contact at the interface of the gate and source/drain electrodes and the metal interconnects, reducing the contact resistance of the electrodes. The silicide materials have been changed from titanium silicide at above 130 nm device dimensions, to cobalt silicide at between 90 nm to 130 nm device dimensions, to nickel silicide at between 65 nm to 90 nm device dimensions, and now to nickel platinum silicide for device dimensions below 65 nm.
Advanced semiconductor fabrication processes currently use nickel and nickel alloy silicide due to their low electrical resistivity, low silicon consumption, good resistance behavior in narrow lines, and low processing temperature. A conventional method of forming a nickel silicide includes depositing a nickel layer on a semiconductor wafer, followed by a first rapid thermal process (RTP) at low temperatures of about 30° C. to react nickel with silicon to produce high resistance nickel silicide phase Ni2Si or NiSi. A selective etching process is performed to remove the unreacted nickel layer, and a second RTP at higher temperatures of about 450 C. is performed to convert high resistance nickel silicide phase Ni2Si or NiSi to low resistance nickel silicide phase NiSi2.
A challenge of nickel silicide is the potential spiking effect, together with possible lateral diffusion to the channel region. Thus nickel alloy silicide, especially nickel platinum silicide, has been used to improve the thermal stability of nickel silicide. For example, nickel platinum silicide with 5 to 10 atomic percent (at %) platinum content can increase the silicide nucleation temperature to 900 C and the agglomeration temperature to 750 C, while still retaining the same conductivity as that of pure nickel silicide. However, platinum is difficult to etch, resulting in potential platinum residue issues during the removal of the unreacted metal layer.
Therefore, etch solutions and methods are needed to effectively remove advanced materials (e.g., nickel and platinum) during semiconductor processing and manufacturing.